There was hardly any fish discarded. The lack of small fish did 

 not provide for a good data base for the use of the covered-tow 

 method. In addition, the covers did not seem to function well. 

 The 72-thread twisted cotton twine that the covers were made 

 of apparently filled up with sand and mud particles, causing 

 the covers to become exceptionally heavy. That, and the fact 

 that our catches were large, tended to cause a masking of the 

 cod ends. We thus switched to alternate tows exclusively on the 

 third day. The basic catch data are presented in Appendix E. 

 There was a small incidental catch of goosefish; wolffish; 

 cusk, Brosme brosme; Illex squid; grey sole; and halibut. 



Atlantic Cod 



The selection factors for Atlantic cod were determined from 

 each experiment's data and from combined data (Tables 2-5, 

 Fig. 3). The range of values of these selection factors falls 

 within the range of those reported by Holden (1971). Assum- 

 ing the true selection factor lies somewhere between those 

 determined from the covered and alternate tow methods, these 

 experiments confirm the average polyamide selection factor of 

 3.6 for Atlantic cod in the North Atlantic reported by Holden 



Experiment Four 



This experiment was conducted from the New Bedford bas- 

 ed fishing vessels Valkyrie and Gen. George S. Patton, 8-11 

 October 1978, in the waters east of Nantucket Shoals (Fig. 2). 

 The experiment consisted of four four-tow series and was per- 

 formed in the same order as Experiment Two. Vessel speed 

 was maintained at 3.0-3.5 kn. 



Thirty meshes were measured after each tow, and means, 

 standard deviations, and standard errors calculated (Appendix 

 C). The small cod ends on the Valkyrie and Patton had mean 

 mesh sizes of 108.3 mm (4.3 in) and 106.0 mm (4.2 in), respec- 

 tively. The large cod end on the Valkyrie averaged 127.4 mm 

 (5.0 in) and on the Patton averaged 134.6 mm (5.3 in). 



During the nonexperimental commercial tows the vessels 

 fished the hard bottom of Nantucket Shoals, making good 

 catches of Atlantic cod and winter flounder. However, they 

 tore up their nets on almost every tow. Since tear-ups in- 

 validate experimental tows, we had to conduct our selectivity 

 experiment on smoother bottom. Here our catches were poor 

 and highly variable. There were very few small fish. 



There were incidental catches of skates, goosefish, sculpins, 

 squid, scallops {Placopecten magellanicus), herring, lobster, 

 and halibut. The Patton hardly caught any Atlantic cod, com- 

 pared with the Valkyrie, on Tows 5, 7, 14, and 16. In one case 

 it can be attributed to a tear-up (Tow 14) and in another case 

 to a foul-up (Tow 16). Both vessels had numerous small 

 "hangs." All the problems added together make the data from 

 experiment four questionable in regard to catch comparisons 

 and selectivity analysis. The reader must keep this in mind 

 when reviewing the following sections. 



RESULTS 



The results of the four experiments worked up on an in- 

 dependent basis can be found in the Woods Hole Laboratory 

 reference series as Laboratory Report No. 78-12, 78-24, 78-48, 

 and 78-54 (Smolowitz et al. 2 " 5 ). What follows is a summary 

 and synthesis of the four experiments on a species basis. 



Table 2. — Atlantic cod selection factor summary. 



'Smolowitz, R. J., D. Arnold, and F. Mirarchi. 1978. New England mesh 

 selectivity studies. Experiment one, inshore groundfish. Northeast Fish. Cent., 

 Woods Hole Lab. Ref. 78-12, 44 p. 



'Smolowitz, R. J., R. Testaverde, and M. DiLiberti. 1978. New England mesh 

 selectivity studies. Experiment two, inshore groundfish. Northeast Fish. Cent., 

 Woods Hole Lab. Ref. 78-24, 82 p. 



'Smolowitz, R. J., A. Brancaleone, and G. Brancaleone. 1978. New England 

 mesh selectivity studies. Experiment three, offshore groundfish. Northeast Fish. 

 Cent., Woods Hole Lab. Ref. 78-48, 39 p. 



'Smolowitz, R. J., L. Sovik, and P. Jacobsen. 1978. New England mesh selec- 

 tivity studies. Experiment four, offshore groundfish. Northeast Fish. Cent., 

 Woods Hole Lab. Ref. 78-54, 31 p. 





Total 

 no. of 



Sel 



ection factor 





Small 



Large 



Alternate 



Experiment 



fish 



mesh 



mesh 



tow 



One 



492 



3.21 



3.31 



3.88 



Two 



2,510 



3.19 



3.37 



3.59 



Three 



686 



— 



— 



4.00 



Four 



2,024 



3.64 



3.74 



3.96 



Combined 



5,712 



3.33 



3.41 



3.80 



Table 3. — Atlantic cod length frequency distribu- 

 tions and percent retained for the small-mesh (105 

 mm overall average) covered tows — all vessels. 



Length 



Numbers caught 





interval 





105 mm 



Percent 



(cm) 



105 mm 



plus covers 



retained 



10-12 











0.0 



13-15 



1 



7 



14.3 



16-18 



2 



27 



7.4 



19-21 



5 



52 



9.6 



22-24 



3 



32 



9.4 



25-27 



7 



26 



26.9 



28-30 



17 



42 



40.5 



31-33 



42 



110 



38.2 



34-36 



104 



181 



57.5 



37-39 



206 



264 



78.0 



40-42 



203 



219 



92.7 



43-45 



220 



226 



97.3 



46-18 



153 



158 



96.8 



49-51 



79 



79 



100.0 



52-54 



109 



111 



98.2 



55-57 



74 



76 



97.4 



58-60 



69 



71 



97.2 



61-63 



46 



46 



100.0 



64-66 



75 



76 



98.7 



67-69 



81 



81 



100.0 



70-72 



82 



82 



100.0 



73-75 



86 



86 



100.0 



76-78 



79 



79 



100.0 



79-81 



53 



53 



100.0 



82-84 



33 



33 



100.0 



85-87 



20 



20 



100.0 



88-90 



12 



12 



100.0 



91-93 



21 



21 



100.0 



94-96 



8 



8 



100.0 



97-99 



12 



12 



100.0 



100-102 



9 



9 



100.0 



103-105 



11 



11 



100.0 



106-108 



4 



4 



100.0 



109-111 



3 



3 



100.0 



112-114 



— 



— 



— 



115-117 



1 



1 



100.0 



118-120 



— 



— 



— 



121-123 



— 



— 



— 



124-126 



1 



1 



100.0 



Totals 



1,931 



2,319 





